This invention relates to a helical-scan type rotating-head magnetic record/reproduce apparatus and, more particularly, to a rotating head PCM record/reproduce apparatus capable of so-called simultaneous monitoring of recorded signals or mixing by after-recording.
The conventional helical-scan rotating-head PCM recorder has the following recorded-signal monitoring mechanism.
As shown in FIG. 1, an analog signal is supplied through an input terminal 1 to an analog-to-digital converter (A/D converter) 2 by which it is converted to a digital signal. This digital signal is supplied through a digital signal processing circuit 3 of the recording system and a recording amplifier 5 to record/reproduce heads 7 by which it is recorded on a magnetic tape 8, and at the same time the digital signal to be recorded, as provided from the circuit 3, is supplied through a line 4, a change-over switch 12, and a digital signal processing circuit 13 of the reproducing system to a digital-to-analog converter (D/A converter) 14 by which the digital signal is converted to an analog signal, which is used as a signal to be monitored. That is, the signal being monitored is not a signal derived from the magnetic tape and reproduced therefrom, but is the signal being recorded thereon. Therefore, this simultaneous monitoring mechanism does not have the function to monitor the presence or absence of dropout and occurrence of errors after reading the recorded signal from the magnetic tape, which is one of the basic objects of the simultaneous monitoring.
On the other hand, in the Ampex-system video tape recorder, a plurality of heads are used and a reproduce head scans the recorded tracks at the time of recording for the purpose of simultaneous monitoring.
However, in the above recorder, since the recording current is continuously supplied to the record head, this recording current interferes with the relatively weak signal from the reproduce head. Thus, in general, to protect the reproduced signal from this interference, a conductor plate is disposed between the supply line for the recording current and the reproduced output line, thereby providing a shielding. This shielding means requires additional manufacturing processes, leading to high cost of the equipment. Also, the shielding effect itself is not practical.